Large quantities of bulk particulate materials such as agricultural crops are often transported through ducts, conduits, pipes and the like to an accumulation area for processing or utilization. It is often desirable to measure the quantity of material during its transport or after it is accumulated. One example where it is desirable to measure the amount of materials is in the area of calculation of agricultural crop yields. The management of contemporary agricultural operations makes it highly advantageous to accurately determine the quantities of crops being harvested from each area within any given field. For example, knowledge of the productivity of individual field areas allows the grower to adjust application of fertilizer, irrigation, and herbicides to maximize crop yields.
Until recently, crop yields have been largely determined on the basis of an entire field, without the ability or the need to obtain information as to the yields in different locations in a field. Generally, crops were recovered, conveyed to a weighing site, weighed with the transporting vehicle or the container, and the weight of the vehicle or container subtracted from the gross weight to obtain the amount of product recovered. This procedure is not dynamic in nature and cannot be adapted to real time collection of data which is necessary for analysis of yields collected from individual field areas.
Systems which can measure crop yields as crops are harvested have been previously used in conjunction with mobile harvesters. Typically, a mobile harvester moves over a field picking crops and simultaneously storing the picked crops in a receptacle mounted on the harvester. One system involves weighing the crop receptacle and the crops in the receptacle as the harvester moves through the field. However, machine dynamics and the large receptacle weight to crop weight ratio lead to serious errors when measurements are made on a real time basis.
A different existing real time measurement system operates by conveying the crops to the receptacle by means of an airstream. The airstream is directed in such a manner that the conveyed material impinges on a pressure plate that is connected to a pressure transducer which creates a real time pressure signal indicative of the amount of materials striking the plate. This permits real time determination of the quantity of material that is flowing into the receptacle, the quantity being proportional to the pressure on the plate. This system is useful because it may be installed on mobile harvesting equipment for the measurement of crop yields as the crops are harvested. Additionally, the real time measurement of crop flow will show interruptions in the crop flow which provide indications of equipment malfunction.
Although this latter system could in theory permit recognition of the quantities of crops recovered from different areas within a field, it is not suitable for use when harvesting certain crops, such as cotton. Cotton and similar crops adhere to the pressure plate, thus inhibiting the flow of the cotton to the receptacle. Additionally, as more cotton accumulates on the pressure plate, inaccurate measurements are taken. Finally, it has been found that the pressure plate system cannot be effectively installed on existing cotton harvesting machinery.
Thus, a need exists for a flow rate sensor which does not impede the flow of entrained material. Furthermore, there is a need for a sensor to accurately obtain real time flow data for entrained material. Also, there is a need for a flow sensor which may be installed on existing cotton harvesting machinery. Finally, a sensor is desired which can correct for errors and maintain accurate data measurements.